It is known to provide an engine with one or more superchargers, which may be embodied in the form of exhaust driven turbochargers. Superchargers usually require a lubrication system and many such lubrication systems are closed circuits often using engine oil as a lubricant. The lubrication system usually includes an oil feed conduit and an oil return conduit. The oil feed supplies oil under pressure from an oil pump of the engine to the or each supercharger concerned and the oil return comprises a conduit adapted to drain the oil away towards a collection area such as an oil sump of the engine. Life expectancy of a turbocharger relies considerably on a steady flow of clean oil supplied to its bearings under pressure from the engine's lubrication system and on the free exit of that oil for its return back to the engine sump.
In U.S. Pat. No. 4,716,735, an exhaust gas driven turbocharger arrangement is proposed in which an engine mounting is integrated with a bearing housing of the turbocharger. Oil supply and return passages are defined through the mounting for use in lubrication of the turbocharger bearings. Such an arrangement requires a custom-made turbocharger in order to integrate its bearing housing with the engine mounting of a particular installation. Custom-made turbochargers may prove more expensive than using mass-produced items.
The arrangement proposed in U.S. Pat. No. 4,716,735 is best suited to use in engine assemblies having only one turbocharger and may not prove suitable for use in an arrangement calling for a plurality of turbochargers. For example, in a multi-cylinder engine having its cylinders arranged in banks in a ‘V’ or ‘W’ configuration, it may be desirable to provide a plurality of turbochargers.
Taking the example of a ‘V’ configured engine and attempting to fit a plurality of turbochargers according to U.S. Pat. No. 4,716,735 dedicated one to each bank, it will be found that a symmetrical set-up is not possible. In order to bolt a second example of the same component to the opposite side of the engine block, the whole turbocharger and integrated mounting assembly of that second example must be rotated 180°. One problem with such an arrangement is that the compressor and exhaust turbines of the opposing turbochargers will point towards opposite ends of the engine. This may lead to complex and less than ideal inlet and exhaust ducting. To reverse the orientation of the turbocharger would require an inverted casting for the bearing housing, resulting in a customized turbocharger on each side of the engine. Rather than reducing piece cost by doubling volume, such an arrangement might prove cost prohibitive as it would significantly increase the investment necessary in producing both right- and left-handed parts. In addition, it would necessitate precautions in parts delivery to the side of the production line, e.g. to ensure smooth delivery of the right parts to the assembly stations affected in equal volumes of each and to their appropriate sides of the line.
In U.S. Pat. No. 4,583,367 an arrangement is proposed for integration of a turbocharger arrangement with an engine mounting. This proposal deals with a single turbocharger and is concerned with defoaming and degassification of the oil being returned to the engine sump. Neither reversibility of the turbo installation between sides of the engine nor twin-turbochargers are considered. Reversing between sides or doubling up on turbochargers would suffer similar problems to those discussed in that respect for U.S. Pat. No. 4,716,735.
EP-1176301 proposes an engine crankcase that includes an integral turbocharger mounting. In similar fashion to U.S. Pat. No. 4,583,367, this document deals only with a single turbocharger and reversibility of the turbocharger installation between sides of the engine or twin-turbochargers are not considered. Reversing between sides or doubling up on turbochargers would suffer similar problems to those discussed in that respect for U.S. Pat. No. 4,716,735
EP-0952329 proposes a single and very complicated casting that acts as a one-piece integrated front-end for a large industrial engine. The use of such a one piece front end is expensive and is cost prohibitive for mass production. Such an arrangement also lacks flexibility in moving the position of the turbochargers around between variations in an engine range. The turbochargers can only be mounted high up on the engine and this makes the arrangement unsuitable for adaptation for use in a passenger vehicle due to the height restrictions inherent in under-hood installations.
DE-10122406 proposes a single carrier casing having two turbocharger mountings integrated into it and adapted to carry a pair of turbochargers. The casting is reversible in its mounting position in co-operation with a manifold arrangement. In similar fashion to EP-0952329, integration of both turbocharger mountings into the same casting largely limits use of this arrangement to mounting the turbochargers on top of the engine. That limits design flexibility and may impose height problems in some under-hood installations, notable for passenger vehicles.
There is therefore a continuing need to seek improved arrangements for mounting multiple superchargers to engines, in particular for use in installations for passenger vehicles.